Biogas is a mixture comprising mainly methane and carbon dioxide. It is produced when organic matter decomposes in the absence of oxygen.(Anaerobic digestion)

Biogas produced in anaerobic digesters consists of

• Methane (50%-80%).
• Carbon dioxide (20%-50%).
• And trace levels of other gases such as hydrogen, carbon monoxide, nitrogen, oxygen, and hydrogen sulfide.
• The relative percentage of these gases in biogas depends on the feed material and management of the process.
• Methane is a gas (CH4). It is the major component of the "natural" gas used in many homes for cooking and heating. It is odorless, colorless, and yields about 1,000 British Thermal Units (Btu) [252 kilocalories (kcal)] of heat energy per cubic foot (0.028 cubic meters) when burned.
• Anaerobic bacteria break down or "digest" organic material in the absence of oxygen and produce 'biogas" as a waste product.
• Anaerobic processes can be managed in a "digester" (an airtight tank) or a covered lagoon (a pond used to store manure) for waste treatment.

Conditions and variable influencing anaerobic digestion:

1- Temperature, the optimum (30-40) usually 35 C
2- PH: the optimal PH range fall {6.6 and 7}
3- Organic material, the amount of gas production depends on feeding material, each material has properties
for example C/N ratio: the relationship between the amount of carbon and nitrogen present in organic material
C/N ratio in anaerobic material between (20 and 30).

Advantages of biogas:

1- Reduce the greenhouse gases
2- Provides as source of energy with no net increase in atmospheric carbon which contribute to climate change.

Disadvantages:
Digester has significant capital and operational cost